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810507fe6f
Once a lock class is zapped, all the lock chains that include the zapped
class are essentially useless. The lock_chain structure itself can be
reused, but not the corresponding chain_hlocks[] entries. Over time,
we will run out of chain_hlocks entries while there are still plenty
of other lockdep array entries available.
To fix this imbalance, we have to make chain_hlocks entries reusable
just like the others. As the freed chain_hlocks entries are in blocks of
various lengths. A simple bitmap like the one used in the other reusable
lockdep arrays isn't applicable. Instead the chain_hlocks entries are
put into bucketed lists (MAX_CHAIN_BUCKETS) of chain blocks. Bucket 0
is the variable size bucket which houses chain blocks of size larger than
MAX_CHAIN_BUCKETS sorted in decreasing size order. Initially, the whole
array is in one chain block (the primordial chain block) in bucket 0.
The minimum size of a chain block is 2 chain_hlocks entries. That will
be the minimum allocation size. In other word, allocation requests
for one chain_hlocks entry will cause 2-entry block to be returned and
hence 1 entry will be wasted.
Allocation requests for the chain_hlocks are fulfilled first by looking
for chain block of matching size. If not found, the first chain block
from bucket[0] (the largest one) is split. That can cause hlock entries
fragmentation and reduce allocation efficiency if a chain block of size >
MAX_CHAIN_BUCKETS is ever zapped and put back to after the primordial
chain block. So the MAX_CHAIN_BUCKETS must be large enough that this
should seldom happen.
By reusing the chain_hlocks entries, we are able to handle workloads
that add and zap a lot of lock classes without the risk of running out
of chain_hlocks entries as long as the total number of outstanding lock
classes at any time remain within a reasonable limit.
Two new tracking counters, nr_free_chain_hlocks & nr_large_chain_blocks,
are added to track the total number of chain_hlocks entries in the
free bucketed lists and the number of large chain blocks in buckets[0]
respectively. The nr_free_chain_hlocks replaces nr_chain_hlocks.
The nr_large_chain_blocks counter enables to see if we should increase
the number of buckets (MAX_CHAIN_BUCKETS) available so as to avoid to
avoid the fragmentation problem in bucket[0].
An internal nfsd test that ran for more than an hour and kept on
loading and unloading kernel modules could cause the following message
to be displayed.
[ 4318.443670] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
The patched kernel was able to complete the test with a lot of free
chain_hlocks entries to spare:
# cat /proc/lockdep_stats
:
dependency chains: 18867 [max: 65536]
dependency chain hlocks: 74926 [max: 327680]
dependency chain hlocks lost: 0
:
zapped classes: 1541
zapped lock chains: 56765
large chain blocks: 1
By changing MAX_CHAIN_BUCKETS to 3 and add a counter for the size of the
largest chain block. The system still worked and We got the following
lockdep_stats data:
dependency chains: 18601 [max: 65536]
dependency chain hlocks used: 73133 [max: 327680]
dependency chain hlocks lost: 0
:
zapped classes: 1541
zapped lock chains: 56702
large chain blocks: 45165
large chain block size: 20165
By running the test again, I was indeed able to cause chain_hlocks
entries to get lost:
dependency chain hlocks used: 74806 [max: 327680]
dependency chain hlocks lost: 575
:
large chain blocks: 48737
large chain block size: 7
Due to the fragmentation, it is possible that the
"MAX_LOCKDEP_CHAIN_HLOCKS too low!" error can happen even if a lot of
of chain_hlocks entries appear to be free.
Fortunately, a MAX_CHAIN_BUCKETS value of 16 should be big enough that
few variable sized chain blocks, other than the initial one, should
ever be present in bucket 0.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200206152408.24165-7-longman@redhat.com
255 lines
6.9 KiB
C
255 lines
6.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* kernel/lockdep_internals.h
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*
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* Runtime locking correctness validator
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*
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* lockdep subsystem internal functions and variables.
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*/
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/*
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* Lock-class usage-state bits:
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*/
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enum lock_usage_bit {
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#define LOCKDEP_STATE(__STATE) \
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LOCK_USED_IN_##__STATE, \
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LOCK_USED_IN_##__STATE##_READ, \
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LOCK_ENABLED_##__STATE, \
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LOCK_ENABLED_##__STATE##_READ,
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#include "lockdep_states.h"
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#undef LOCKDEP_STATE
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LOCK_USED,
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LOCK_USAGE_STATES
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};
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#define LOCK_USAGE_READ_MASK 1
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#define LOCK_USAGE_DIR_MASK 2
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#define LOCK_USAGE_STATE_MASK (~(LOCK_USAGE_READ_MASK | LOCK_USAGE_DIR_MASK))
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/*
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* Usage-state bitmasks:
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*/
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#define __LOCKF(__STATE) LOCKF_##__STATE = (1 << LOCK_##__STATE),
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enum {
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#define LOCKDEP_STATE(__STATE) \
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__LOCKF(USED_IN_##__STATE) \
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__LOCKF(USED_IN_##__STATE##_READ) \
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__LOCKF(ENABLED_##__STATE) \
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__LOCKF(ENABLED_##__STATE##_READ)
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#include "lockdep_states.h"
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#undef LOCKDEP_STATE
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__LOCKF(USED)
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};
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#define LOCKDEP_STATE(__STATE) LOCKF_ENABLED_##__STATE |
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static const unsigned long LOCKF_ENABLED_IRQ =
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#include "lockdep_states.h"
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0;
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#undef LOCKDEP_STATE
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#define LOCKDEP_STATE(__STATE) LOCKF_USED_IN_##__STATE |
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static const unsigned long LOCKF_USED_IN_IRQ =
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#include "lockdep_states.h"
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0;
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#undef LOCKDEP_STATE
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#define LOCKDEP_STATE(__STATE) LOCKF_ENABLED_##__STATE##_READ |
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static const unsigned long LOCKF_ENABLED_IRQ_READ =
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#include "lockdep_states.h"
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0;
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#undef LOCKDEP_STATE
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#define LOCKDEP_STATE(__STATE) LOCKF_USED_IN_##__STATE##_READ |
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static const unsigned long LOCKF_USED_IN_IRQ_READ =
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#include "lockdep_states.h"
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0;
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#undef LOCKDEP_STATE
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#define LOCKF_ENABLED_IRQ_ALL (LOCKF_ENABLED_IRQ | LOCKF_ENABLED_IRQ_READ)
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#define LOCKF_USED_IN_IRQ_ALL (LOCKF_USED_IN_IRQ | LOCKF_USED_IN_IRQ_READ)
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#define LOCKF_IRQ (LOCKF_ENABLED_IRQ | LOCKF_USED_IN_IRQ)
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#define LOCKF_IRQ_READ (LOCKF_ENABLED_IRQ_READ | LOCKF_USED_IN_IRQ_READ)
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/*
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* CONFIG_LOCKDEP_SMALL is defined for sparc. Sparc requires .text,
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* .data and .bss to fit in required 32MB limit for the kernel. With
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* CONFIG_LOCKDEP we could go over this limit and cause system boot-up problems.
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* So, reduce the static allocations for lockdeps related structures so that
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* everything fits in current required size limit.
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*/
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#ifdef CONFIG_LOCKDEP_SMALL
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/*
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* MAX_LOCKDEP_ENTRIES is the maximum number of lock dependencies
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* we track.
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*
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* We use the per-lock dependency maps in two ways: we grow it by adding
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* every to-be-taken lock to all currently held lock's own dependency
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* table (if it's not there yet), and we check it for lock order
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* conflicts and deadlocks.
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*/
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#define MAX_LOCKDEP_ENTRIES 16384UL
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#define MAX_LOCKDEP_CHAINS_BITS 15
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#define MAX_STACK_TRACE_ENTRIES 262144UL
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#define STACK_TRACE_HASH_SIZE 8192
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#else
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#define MAX_LOCKDEP_ENTRIES 32768UL
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#define MAX_LOCKDEP_CHAINS_BITS 16
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/*
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* Stack-trace: tightly packed array of stack backtrace
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* addresses. Protected by the hash_lock.
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*/
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#define MAX_STACK_TRACE_ENTRIES 524288UL
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#define STACK_TRACE_HASH_SIZE 16384
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#endif
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/*
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* Bit definitions for lock_chain.irq_context
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*/
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#define LOCK_CHAIN_SOFTIRQ_CONTEXT (1 << 0)
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#define LOCK_CHAIN_HARDIRQ_CONTEXT (1 << 1)
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#define MAX_LOCKDEP_CHAINS (1UL << MAX_LOCKDEP_CHAINS_BITS)
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#define MAX_LOCKDEP_CHAIN_HLOCKS (MAX_LOCKDEP_CHAINS*5)
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extern struct list_head all_lock_classes;
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extern struct lock_chain lock_chains[];
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#define LOCK_USAGE_CHARS (1+LOCK_USAGE_STATES/2)
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extern void get_usage_chars(struct lock_class *class,
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char usage[LOCK_USAGE_CHARS]);
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extern const char *__get_key_name(const struct lockdep_subclass_key *key,
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char *str);
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struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i);
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extern unsigned long nr_lock_classes;
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extern unsigned long nr_zapped_classes;
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extern unsigned long nr_zapped_lock_chains;
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extern unsigned long nr_list_entries;
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long lockdep_next_lockchain(long i);
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unsigned long lock_chain_count(void);
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extern unsigned long nr_stack_trace_entries;
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extern unsigned int nr_hardirq_chains;
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extern unsigned int nr_softirq_chains;
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extern unsigned int nr_process_chains;
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extern unsigned int nr_free_chain_hlocks;
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extern unsigned int nr_lost_chain_hlocks;
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extern unsigned int nr_large_chain_blocks;
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extern unsigned int max_lockdep_depth;
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extern unsigned int max_bfs_queue_depth;
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#ifdef CONFIG_PROVE_LOCKING
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extern unsigned long lockdep_count_forward_deps(struct lock_class *);
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extern unsigned long lockdep_count_backward_deps(struct lock_class *);
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#ifdef CONFIG_TRACE_IRQFLAGS
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u64 lockdep_stack_trace_count(void);
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u64 lockdep_stack_hash_count(void);
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#endif
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#else
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static inline unsigned long
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lockdep_count_forward_deps(struct lock_class *class)
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{
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return 0;
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}
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static inline unsigned long
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lockdep_count_backward_deps(struct lock_class *class)
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{
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return 0;
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}
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#endif
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#ifdef CONFIG_DEBUG_LOCKDEP
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#include <asm/local.h>
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/*
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* Various lockdep statistics.
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* We want them per cpu as they are often accessed in fast path
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* and we want to avoid too much cache bouncing.
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*/
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struct lockdep_stats {
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unsigned long chain_lookup_hits;
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unsigned int chain_lookup_misses;
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unsigned long hardirqs_on_events;
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unsigned long hardirqs_off_events;
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unsigned long redundant_hardirqs_on;
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unsigned long redundant_hardirqs_off;
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unsigned long softirqs_on_events;
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unsigned long softirqs_off_events;
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unsigned long redundant_softirqs_on;
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unsigned long redundant_softirqs_off;
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int nr_unused_locks;
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unsigned int nr_redundant_checks;
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unsigned int nr_redundant;
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unsigned int nr_cyclic_checks;
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unsigned int nr_find_usage_forwards_checks;
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unsigned int nr_find_usage_backwards_checks;
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/*
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* Per lock class locking operation stat counts
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*/
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unsigned long lock_class_ops[MAX_LOCKDEP_KEYS];
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};
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DECLARE_PER_CPU(struct lockdep_stats, lockdep_stats);
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extern struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
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#define __debug_atomic_inc(ptr) \
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this_cpu_inc(lockdep_stats.ptr);
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#define debug_atomic_inc(ptr) { \
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WARN_ON_ONCE(!irqs_disabled()); \
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__this_cpu_inc(lockdep_stats.ptr); \
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}
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#define debug_atomic_dec(ptr) { \
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WARN_ON_ONCE(!irqs_disabled()); \
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__this_cpu_dec(lockdep_stats.ptr); \
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}
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#define debug_atomic_read(ptr) ({ \
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struct lockdep_stats *__cpu_lockdep_stats; \
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unsigned long long __total = 0; \
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int __cpu; \
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for_each_possible_cpu(__cpu) { \
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__cpu_lockdep_stats = &per_cpu(lockdep_stats, __cpu); \
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__total += __cpu_lockdep_stats->ptr; \
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} \
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__total; \
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})
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static inline void debug_class_ops_inc(struct lock_class *class)
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{
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int idx;
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idx = class - lock_classes;
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__debug_atomic_inc(lock_class_ops[idx]);
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}
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static inline unsigned long debug_class_ops_read(struct lock_class *class)
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{
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int idx, cpu;
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unsigned long ops = 0;
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idx = class - lock_classes;
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for_each_possible_cpu(cpu)
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ops += per_cpu(lockdep_stats.lock_class_ops[idx], cpu);
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return ops;
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}
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#else
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# define __debug_atomic_inc(ptr) do { } while (0)
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# define debug_atomic_inc(ptr) do { } while (0)
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# define debug_atomic_dec(ptr) do { } while (0)
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# define debug_atomic_read(ptr) 0
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# define debug_class_ops_inc(ptr) do { } while (0)
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#endif
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